1. Field of the Invention
The present invention pertains to a stepping motor and to a taking lens barrel for a camera incorporating said stepping motor as a drive source for the shutter mechanisms or diaphragm mechanisms.
2. Description of the Related Art
Conventionally, one major aspect of the desire for increased camera compactness has been the trend toward increasingly compact lens barrel units. For example, as shown in FIG. 9, stepping motor 86 is used as an actuator to rotate rotatable ring 84 that opens and closes diaphragm blades 82 placed inside lens barrel unit 80 (see, e.g., Japanese Laid-Open Patent Application Hei 1-101527). An example of another conventional lens barrel unit having fewer parts than the conventional stepping motor 86 described above is shown in FIG. 7, which shows the construction and arrangement of the mechanism of stepping motor 51 inside conventional lens barrel unit 50, and FIG. 8 shows a cross-section of the mechanism in FIG. 7 cut along the VIII--VIII line. Stepping motor 51 comprises (i) essentially cylindrical rotor 53 (which is polarized to have multiple polarities along its circumference) that is rotatably supported by supporting members 52 fixed inside lens barrel 50, and (ii) horseshoe-shaped stators 54 that face each other across rotor 53. Because stepping motor 51 is placed at a position that is outside and around lens 55 so as not to hinder the image recording operation, reducing the size of lens barrel unit 50 without changing the diameter of lens 55 depends on how the size of stepping motor 51 is reduced.
The example of FIG. 7 is an example in which space is used more efficiently by curving yokes 56 of horseshoe-shaped stators 54 into arches along the circumference of lens barrel 50. In order to further reduce the size of the stepping motor, it is necessary to reduce the diameter of rotor 53 and to reduce the gaps between stator teeth 56a and 56b of yokes 56. However, that would entail the problem that the pressing of yokes 56 would become difficult and the manufacturing cost would increase. In addition, when the need for preserving the space for the winding of coils 57 is taken into account, the gaps between stator teeth 56a and 56b of yokes 56 cannot be reduced beyond a certain degree. It is therefore concluded that only limited compactness can be achieved if the construction described above is used.
Consequently, the technological problem to be resolved by the present invention is to reduce the size of the stepping motor through a creative configuration of the yokes and to reduce the size of the camera lens barrel through the use of said reduced-size stepping motor.